We estimated carbon stock of mangrove Kandelia obovata Sheue, Liu & Yong and Sonneratia caseolaris (L.) Engler planted in coastal zone of Red River Delta, Vietnam. A total of 84 10 x 10 m sample plots consisting of 39 K. obovata at 1-13 years old, 33 S. caseolaris at 2-7, 8-13 years old and mixed species of K. bovata and S. caseolaris at 10-13 years old were established. A tree census was carried out in the sample plots. Diameter at 30 cm above widening base of trunk of all trees were measured. Allometric equations WAG = 0.000318D4.19917, WBG = 0.000431D3.56175 and WTT = 0.000596D4.04876 were used to estimate above ground, below ground and total tree biomass for K. obovata. Allometric equations WAG = 0.04975D1.94748, WBG = 0.01420D2.12146 and WTT = 0.10316D1.85845 were used to estimate above ground, below ground and total tree biomass for S. caseolaris. Those allometric equations were established from meassurements of 101 K. obovata trees and 84 S. caseolaris trees. The results indicates that above ground, below ground and total standing tree biomass of K. obovata and S. caseolaris increased with stand. Standing tree biomass of K. obovata was consistenly higher than those of S. caseolaris or mixture of both species.